A seat for a passenger of a vehicle, for example, is comprised of a seat cushion and a seatback. The seat cushion is comprised of a seating part and cushion part sides support projecting upward from lateral ends of the seating part. The seatback is comprised of a backrest part and a seatback part side supports projecting forward from lateral ends of the backrest part. Each side support is provided to extend along a passenger body so as to keep a seated passenger in good or desired posture. The thus-explained seat is disclosed in JP 2014-000323 A, for example.
In the seat disclosed in JP 2014-000323 A, a cushion material is covered with a skin. The skin is held in tight contact with the cushion material.
However, prolonged-time use of such a seat causes certain problems. One problem is that the side supports opens outwardly in a seat width direction as a result of wear-out of the side supports. The skin often wears out due to the friction generated by repeated seating of the passenger on the seat.